[PATCH v5 1/6] arm64: kprobe: add checks for ARMv8.3-PAuth combined instructions
Dave Martin
Dave.Martin at arm.com
Wed Sep 2 11:39:04 EDT 2020
On Tue, Aug 18, 2020 at 12:41:06PM +0530, Amit Daniel Kachhap wrote:
> Currently the ARMv8.3-PAuth combined branch instructions (braa, retaa
> etc.) are not simulated. However the uprobe of such instructions leads
> to kernel warnings in a loop as they are not explicitly checked.
>
> This is fixed by adding definitions of all such instructions and
> rejecting their probes.
For my understanding, this patch addresses that fact that uprobes
expects the pc to be at xol_addr + 4 after a stepped instruction, except
for branch instructions that it explicitly knows about?
If so, this indeed makes sense as a fix to the existing code.
LDRAA/LDRAB are not affected by this, right?
I'm wondering what happens if these generate an FPAC exception rather
than the data abort that would be expected in v8.3. I think the ptrauth
enhancements allow this, but don't require it.
If uprobes can't cope with SIGILLs in xol instructions then we probably
have bigger problems.
I _think_ the logic in handle_singlestep(), uprobe_deny_signal(),
arch_uprobe_xol_was_trapped() etc. does handle this scenario, but I
confess I don't fully understand all the details of it.
Modulo that:
Reviewed-by: Dave Martin <Dave.Martin at arm.com>
Cheers
---Dave
>
> Warning log:
> WARNING: CPU: 5 PID: 249 at arch/arm64/kernel/probes/uprobes.c:182 uprobe_single_step_handler+0x34/0x50
> Modules linked in:
> CPU: 5 PID: 249 Comm: func Tainted: G W 5.8.0-rc4-00005-ge658591d66d1-dirty #160
> Hardware name: Foundation-v8A (DT)
> pstate: 204003c9 (nzCv DAIF +PAN -UAO BTYPE=--)
> pc : uprobe_single_step_handler+0x34/0x50
> lr : single_step_handler+0x70/0xf8
> sp : ffff800012afbe30
> x29: ffff800012afbe30 x28: ffff000879f00ec0
> x27: 0000000000000000 x26: 0000000000000000
> x25: 0000000000000000 x24: 0000000000000000
> x23: 0000000060001000 x22: 00000000cb000022
> x21: ffff800011fc5a68 x20: ffff800012afbec0
> x19: ffff800011fc86c0 x18: 0000000000000000
> x17: 0000000000000000 x16: 0000000000000000
> x15: 0000000000000000 x14: 0000000000000000
> x13: 0000000000000000 x12: 0000000000000000
> x11: 0000000000000000 x10: 0000000000000000
> x9 : ffff800010085d50 x8 : 0000000000000000
> x7 : 0000000000000000 x6 : ffff800011fba9c0
> x5 : ffff800011fba000 x4 : ffff800012283070
> x3 : ffff8000100a78e0 x2 : 00000000004005f0
> x1 : 0000fffffffff008 x0 : ffff800012afbec0
> Call trace:
> uprobe_single_step_handler+0x34/0x50
> single_step_handler+0x70/0xf8
> do_debug_exception+0xb8/0x130
> el0_sync_handler+0x7c/0x188
> el0_sync+0x158/0x180
>
> Fixes: 74afda4016a7 ("arm64: compile the kernel with ptrauth return address signing")
> Fixes: 04ca3204fa09 ("arm64: enable pointer authentication")
> Signed-off-by: Amit Daniel Kachhap <amit.kachhap at arm.com>
> ---
> Changes since v4:
> * New patch.
>
> arch/arm64/include/asm/insn.h | 12 ++++++++++++
> arch/arm64/kernel/insn.c | 14 ++++++++++++--
> arch/arm64/kernel/probes/decode-insn.c | 4 +++-
> 3 files changed, 27 insertions(+), 3 deletions(-)
>
> diff --git a/arch/arm64/include/asm/insn.h b/arch/arm64/include/asm/insn.h
> index 0bc46149e491..324234068fee 100644
> --- a/arch/arm64/include/asm/insn.h
> +++ b/arch/arm64/include/asm/insn.h
> @@ -359,9 +359,21 @@ __AARCH64_INSN_FUNCS(brk, 0xFFE0001F, 0xD4200000)
> __AARCH64_INSN_FUNCS(exception, 0xFF000000, 0xD4000000)
> __AARCH64_INSN_FUNCS(hint, 0xFFFFF01F, 0xD503201F)
> __AARCH64_INSN_FUNCS(br, 0xFFFFFC1F, 0xD61F0000)
> +__AARCH64_INSN_FUNCS(braaz, 0xFFFFFC1F, 0xD61F081F)
> +__AARCH64_INSN_FUNCS(brabz, 0xFFFFFC1F, 0xD61F0C1F)
> +__AARCH64_INSN_FUNCS(braa, 0xFFFFFC00, 0xD71F0800)
> +__AARCH64_INSN_FUNCS(brab, 0xFFFFFC00, 0xD71F0C00)
> __AARCH64_INSN_FUNCS(blr, 0xFFFFFC1F, 0xD63F0000)
> +__AARCH64_INSN_FUNCS(blraaz, 0xFFFFFC1F, 0xD63F081F)
> +__AARCH64_INSN_FUNCS(blrabz, 0xFFFFFC1F, 0xD63F0C1F)
> +__AARCH64_INSN_FUNCS(blraa, 0xFFFFFC00, 0xD73F0800)
> +__AARCH64_INSN_FUNCS(blrab, 0xFFFFFC00, 0xD73F0C00)
> __AARCH64_INSN_FUNCS(ret, 0xFFFFFC1F, 0xD65F0000)
> +__AARCH64_INSN_FUNCS(retaa, 0xFFFFFFFF, 0xD65F0BFF)
> +__AARCH64_INSN_FUNCS(retab, 0xFFFFFFFF, 0xD65F0FFF)
> __AARCH64_INSN_FUNCS(eret, 0xFFFFFFFF, 0xD69F03E0)
> +__AARCH64_INSN_FUNCS(eretaa, 0xFFFFFFFF, 0xD69F0BFF)
> +__AARCH64_INSN_FUNCS(eretab, 0xFFFFFFFF, 0xD69F0FFF)
> __AARCH64_INSN_FUNCS(mrs, 0xFFF00000, 0xD5300000)
> __AARCH64_INSN_FUNCS(msr_imm, 0xFFF8F01F, 0xD500401F)
> __AARCH64_INSN_FUNCS(msr_reg, 0xFFF00000, 0xD5100000)
> diff --git a/arch/arm64/kernel/insn.c b/arch/arm64/kernel/insn.c
> index a107375005bc..27d5a52d5058 100644
> --- a/arch/arm64/kernel/insn.c
> +++ b/arch/arm64/kernel/insn.c
> @@ -176,7 +176,7 @@ bool __kprobes aarch64_insn_uses_literal(u32 insn)
>
> bool __kprobes aarch64_insn_is_branch(u32 insn)
> {
> - /* b, bl, cb*, tb*, b.cond, br, blr */
> + /* b, bl, cb*, tb*, ret*, b.cond, br*, blr* */
>
> return aarch64_insn_is_b(insn) ||
> aarch64_insn_is_bl(insn) ||
> @@ -185,9 +185,19 @@ bool __kprobes aarch64_insn_is_branch(u32 insn)
> aarch64_insn_is_tbz(insn) ||
> aarch64_insn_is_tbnz(insn) ||
> aarch64_insn_is_ret(insn) ||
> + aarch64_insn_is_retaa(insn) ||
> + aarch64_insn_is_retab(insn) ||
> aarch64_insn_is_br(insn) ||
> aarch64_insn_is_blr(insn) ||
> - aarch64_insn_is_bcond(insn);
> + aarch64_insn_is_bcond(insn) ||
> + aarch64_insn_is_braaz(insn) ||
> + aarch64_insn_is_brabz(insn) ||
> + aarch64_insn_is_braa(insn) ||
> + aarch64_insn_is_brab(insn) ||
> + aarch64_insn_is_blraaz(insn) ||
> + aarch64_insn_is_blrabz(insn) ||
> + aarch64_insn_is_blraa(insn) ||
> + aarch64_insn_is_blrab(insn);
> }
>
> int __kprobes aarch64_insn_patch_text_nosync(void *addr, u32 insn)
> diff --git a/arch/arm64/kernel/probes/decode-insn.c b/arch/arm64/kernel/probes/decode-insn.c
> index 263d5fba4c8a..f9eb8210d6d3 100644
> --- a/arch/arm64/kernel/probes/decode-insn.c
> +++ b/arch/arm64/kernel/probes/decode-insn.c
> @@ -29,7 +29,9 @@ static bool __kprobes aarch64_insn_is_steppable(u32 insn)
> aarch64_insn_is_msr_imm(insn) ||
> aarch64_insn_is_msr_reg(insn) ||
> aarch64_insn_is_exception(insn) ||
> - aarch64_insn_is_eret(insn))
> + aarch64_insn_is_eret(insn) ||
> + aarch64_insn_is_eretaa(insn) ||
> + aarch64_insn_is_eretab(insn))
> return false;
>
> /*
> --
> 2.17.1
>
>
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